1. Field of the Invention
The present invention relates to a hard disc drive (HDD) and a servo signal writing apparatus which are both suitable for detecting the head position.
2. Description of the Related Art
External control type hard disc drives are known to write a servo signal as follows:
A head arm is secured to a moving body provided outside the casing of the hard disc drive and a motion of the moving body is detected by means of some suitable methods, such as a light interference method or the like. Then, on the basis of detected results, the position of the head arm is controlled, i.e., the writing of the servo signal is controlled.
Further, there are known other hard disc drives which include a mirror attached to a head arm to detect the position of the head on the basis of motion of the mirror or other hard disc drives in which a rotary encoder and an optical system for detecting the head position are disposed within the casing thereof.
Hard disc drives are miniaturized more and hence rigidity of the head is decreased, which causes the external control type of hard disc drive to deform the head arm thereof. Also, conditions of the hard disc drives are different when in use and when in the recording mode. There is the disadvantage that a servo signal cannot be written with high accuracy as expected.
According to the above-mentioned other hard drive drives in which the mirror is attached to the head, a load applied to the head tends to change the condition of the head when in the recording mode and in use. As a result, accuracy in the writing of servo signal cannot be increased as expected and resolution also is lowered.
Further, according to the above-mentioned other type of hard disc drives in which the rotary encoder and the like are disposed within the casing, the cost of optical parts is increased.